FAQ - High voltage wire and wiring.

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Richard Hull
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FAQ - High voltage wire and wiring.

Post by Richard Hull » Sun Jul 31, 2016 9:19 pm

Seems this subject never had it's own FAQ. Here goes.

Really good high voltage wire rated above 20 kv is a great rarity. The best general substitute on the cheap is special neon sign, high tension wire. However the best is the snow white silicone wire which is traditionally very expensive. I found an ugly, fat, x-ray cable on the ground at a hamfest and it was rated at 100kv. This 1 inch diameter hog cable cost me $4.00 for a 20 foot length.

For fusor work, the current handling capacity of any properly rated high voltage wire or cable is a complete non-issue. In short, any properly rated HV wire you will ever obtain will carry all the current needed to do nuclear fusion in your fusor!

You will all notice, I use white, 30kv silicone wire on fusor IV. It easily handles 40kv plus, naked in air. To get the single length of this wire from my modified X-ray supply, I ran it in 1" diameter white PVC plumbing pipe. (seen in all imiages of fusor IV). The last foot or so drops, in air, to the fusor's top terminal.

The key to 25kv and higher HV wiring of a supply and all metering is to never expose any HV component within the supply to air! keep everything under oil with good clearances.

Leave the oil filled supply with a single length of proper HV rated silicone wire to the HV terminal on the fusor.

The rules for ultra-safe power supply construction and connection:

1. Keep every HV component in the supply under oil.
2. Keep all HV metering resistors under oil as well. Only the low voltage leads from the divider need to exit the oil.
3. Never, ever attempt to splice any HV cable in air.
4. Use only a single continuous, properly rated HV wire or cable from the supply's output insulator to the fusor's HV terminal.
5. It is wise to run such wire in a grounded conduit, if metal, or, better still, plastic pipe to avoid arcing as the cable runs to the fusor. (double insulation)
6. All air connections should have a toroid, ball or other regularly cleaned voltage stress distribution item at the air joint.
7. Any sharp metallic point in an air connection should be totally engulfed in a heavy wad of high voltage silicone putty.

The above applies to any home brew supply at or over 30kv.

Few here have the materials or know-how to manufacture their own suitable fusor HV supply over 30kv. But all will need to run a high voltage cable from their supply to the fusor.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Bob Reite
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Re: FAQ - High voltage wire and wiring.

Post by Bob Reite » Thu Aug 04, 2016 5:23 am

It is possible to build the entire high voltage supply in air as I have done with my 60 KV supply (maximum, I usually run between 40 KV and 45 KV), but the components used must be rated for use in air. Back in the day of CRT color television sets, "Second Anode" wire that was rated for 40 KV DC was commonly available. It usually has a red outer jacket with a clear or white inner insulation. Some of this cable might turn up at hamfests and would be perfectly adequate for the typical amateur fusor.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.

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Richard Hull
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Re: FAQ - High voltage wire and wiring.

Post by Richard Hull » Thu Aug 04, 2016 5:55 am

I have seen well designed supplies in the 80kv class in air most of this effort was in a quadrupler and at every single point, (electrical connection diode to capacitors), There was a 1 inch diameter solid brass threaded ball. Components spread out and supported well in air can take a lot of electrical tension provided every normally naked point has a high tension relief element. All well made mutltipliers in today's electronics are either potted in some fashion, under oil, or built within metallic toroidal structures to offer field control. For voltages up to 40kv or even more, the balls and toroids are not needed provided every joint has a suitably large wad of silicone HV putty to wrap it up free of air at sharp edges.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Dennis P Brown
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Re: FAQ - High voltage wire and wiring.

Post by Dennis P Brown » Thu Aug 04, 2016 12:17 pm

While I agree building a high voltage (HV) power supply (PS) with all connections in the air can be done if one is careful, creating such exposed wiring in a HV PS over 25 kV is tricky as Richard pointed out. On the other hand, when most of the connections are under oil, the wiring/components are not just safer but also inexpensive wire as well as normal connectors can be used. Aside: synthetic motor oil works great and is rather inexpensive and easy to obtain. For "oil tanks", I use old plastic slide shelves that are designed to hold "nuts and bolts" and and for larger situations, small plastic Tupperware like square bowels. I glue these items down using silicone seal "glue". I also like wood for larger shelves to mount these tanks, transformer, and major items in the case since drilling and adding screws are easier than plexiglas. I prefer plexiglas for under oil mounting in the tanks.

I have one high voltage PS connection in the "air" still in my case. Yes, it uses a "ball" to prevent corona issues but I intend to change that and place it under oil (it is a dangerous exposed HV source when the case is open.) I also rewired all 120 AC connections using a "bus" bar system to get these low voltage wires well away from my HV section. This also has the added advantages of making changes/upgrades far easier since standard "Hot", "Neutral", and "Ground" posts are available and marked (Also, looking at this bus I now know instantly what every wire does/goes to without tracing) and even helps prevent miss connections (darn, happened!)

For instance, adding a master power switch is easy to do because the main wiring is in the same location and accessible. So, design is also rather important for a HV power supply besides laying out the wiring and just connecting components. This gets to the issue of starting from day one and designing the HV PS with the connector system one needs - if one decides to use oil "tanks" for key connections/components, then one needs to make room at the beginning. Adding these after the fact can be a real issue if all the main components are already mounted in place. More critically - repairs. If connections/components are "buried", removal and cleaning are a real pain. Oil isn't anywhere near the same issue. My connection/components are mounted on plastic plates sunk in oil. I lift them up, drain them, and then easily remove them. A quick alcohol rinse and they are ready to work on.

My two cents.

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Re: FAQ - High voltage wire and wiring.

Post by Rex Allers » Thu Aug 04, 2016 10:35 pm

Richard said,
All well made mutltipliers in today's electronics are either potted in some fashion, under oil, or built within metallic toroidal structures to offer field control.
I just thought I would point out a contrary case. All the Glassman HV supplies I have seen have their HV multiplier sections mostly air insulated. The circuits look to be made on standard fiberglass circuit board, but also have many cut-out gaps to break the shortest direct path across the board. All connection points seem to be standard foil pads with rounded corners. Where components are connected, a lot of solder is used to form a rounded blob for no sharp points. The whole multiplier unit is then enclosed in a thick molded plastic case with only one lower-potential end open.

This link from 2007 has pictures that show the internals of a typical unit as I have described.
"Reversing a Glassman Multiplier" by Wilfried Heil
viewtopic.php?f=11&t=4622

This is not to suggest that members should build their own supplies this way, just that one manufacturer is doing it without big ball connection points or potting or oil. I'm sure they have taken care to consider all the electric fields created in their design. Putting HV circuits in oil probably remains good advice for most who might build their own.
Rex Allers

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Richard Hull
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Re: FAQ - High voltage wire and wiring.

Post by Richard Hull » Fri Aug 05, 2016 4:14 am

The rectangular holes tell the story. They re part of the stress relief between the smoothed over pads. Pads are a sharp point regardless of what you do with solder and arcs along boards of smooth flat surface are normal and regular. Using the rectangular holes avoids this, breaking the board's inline surface between pads where capacitance is soldered. One might mistake these for cooling or ventilation holes. They are not.

Clever design. Needless to say, this board must be enclosed and made proof against its environment as over time, dirt and grime would build up due to electrostatic attraction. This would create an arc.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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